It has long been desired to measure the anterior surface of the cornea, initially for providing an objective measurement of the patient's anterior cornea astigmatism. Herman von Helmholtz, in the 19th Century, developed the first keratometer and other investigators improved this device to make the instruments that are in clinical use today. These early developments and the principles of operation of the keratometer are described in R. Mohrman, "The Keratometer," in T. D. Duane (ed.), Clinical Ophthalmology, Vol. 1, Chap. 60, pages 1-12.
In recent years, corneal contact measurement has become of increasing importance in connection with the fitting of contact lenses. In addition to the keratometer, the area of the cornea has been studied with the photokeratometer, stereophotogrammetry, autocollimation keratometers, contact lens and fluorescein methods, interferometry, holographic techniques, moire fringe topography, and profile methods. However, these apparatuses and techniques have not been entirely satisfactory. For example, J. J. Rowsey, Topographical Analysis, describes the deficiencies of these techniques and proposes the use of the photokeratoscope. Unfortunately, even this latter device has the disadvantages of inducing aberrations about the visual axis and requiring the talents of an experienced photographer. See J. J. Rowsey et al., Arch. Ophthalmol. 99, June 1981, p. 1093.